Forming tool tightens spring accuracy

Companies manufacturing such products as small clutches, brakes, and valves sometimes have problems finding precision springs that operate consistently. Due to inconsistencies in wirefeed stock and normal forming-tool wear, spring manufacturing is not an

With its piezo-based forming technology, Reell holds spring tolerances to within ±0.0005 in.

A piezo-based tool controls spring diameter and compensates for wear in Reell s spring-winding process.


Companies manufacturing such products as small clutches, brakes, and valves sometimes have problems finding precision springs that operate consistently. Due to inconsistencies in wirefeed stock and normal forming-tool wear, spring manufacturing is not an exact science. That is, until now.

A computer-controlled spring-forming tool, developed by the Spring Technologies division of Reell Precision Manufacturing, not only adjusts for wear in real time but also compensates for material inconsistencies. The resulting process reportedly forms precision springs with an accuracy better than conventional means for more consistent products and reduced component costs.

While the process was developed for Reell's clutches, it is an important tool for manufacturing precision coil springs in OEM applications involving medical devices, scientific instruments, testing equipment, and precision automotive components.

Reell's process uses an electronic position-control loop and piezoelectrically controlled coiling tool that permits the spring-winding machine to monitor and adjust spring diameters 400 times/sec while it is formed. Until this development, the company controlled spring tolerances by sorting after production — a quality-control method that resulted in waste and high manufacturing costs.

To dynamically measure coils during manufacture, a linear variable-displacement transducer (LVDT) contacts the coil and sends a signal to the computer controlling the process. The computer compares this measurement reading with a programmed value using a proportional integral derivative loop in its software and sends a correction signal. This signal gets amplified and sent to a piezoelectric device embedded in the coiling tool. "These corrections occur much faster than with mechanically controlled systems," says Sean Frost, manager of the Spring Technologies business unit. "Once the tool is properly set up, the micro-positioning action takes over and removes most of the variability from the spring-forming process."

Reell Precision Manufacturing
St. Paul
reellsprings.com

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